These days, it’s a given that the latest web service you sign up for is going to be using email for something. The better services make these messages interactive — when someone leaves a message on your Facebook Wall, you don’t have to head back to Facebook.com to respond; you can just reply to that email message. Unfortunately, from a development standpoint, this is a bit easier said than done.

Mailgun is a new service launching today that wants to make this kind of functionality easy to implement: it offers a ‘Mailbox API’ that lets you bake Email functionality into your application. The service is now open to the public, and the first 50 people to register with the signup code ‘TCRUNCH’ will be entered into a drawing for a new Macbook Air.

So what exactly is Mailgun for? Well, it’s certainly possible to use Mailgun to send notifications, newsletters, or whatever other content you want to distribute on a broad scale — but there are already other services that can perform these tasks. Mailgun differentiates itself with features that extend beyond just sending messages.

The most obvious usecases are for the interactive Email notifications described above. Beyond these notifications, CEO Ev Kontsevoy gave me a few examples illustrating how a developer might put Mailgun to work.

Say a developer wants to offer a mobile game where every user can submit their moves and accompanying photos via Email. Mailgun would allow the developer to programmatically create a mailbox for each user, allowing users to send in these commands, with the added benefit of having an automatic archive of each message that’s submitted.

A service like Stickybits, which lets you create virtual presences for real-world objects by sticking a barcode sticker on them, could set up a mailbox for each real-world object. It would then be possible for users to simply send a photo or message to this email address, in case they had a phone without a barcode scanner app.

As with other API-based services, Mailgun’s success will really come down to demand — how many developers are looking to outsource these tasks, and how many are willing to pay for it? Given how ubiquitous email is, I think Mailgun has a fighting chance, provided their service proves to be reliable (and saves developers as much time as they say it will).